arXiv subjects

C. Trallero-Giner

Publications and source records attributed to C. Trallero-Giner.

23 records · Page 2Linked to original sources

arXiv1999

Thermodynamic functions within the van Hove BCS model: Symmetry mixing effects

All the new layer perovskite superconductors seem to show a phenomenon of symmetry mixing with repect to the order parameter. An analysis of the different alternative of mixing and how far could them be presented is carried out. For the particular case of s+id symmetry of the gap, the temperature dependence of the specific heat ($C_{es}$) and the thermodynamic critical magnetic field ($H_{c}$) are calculated. A double peak transition is observed on $C_{es}(T)$ in the mixed regime while the single peak behavior is recovered for a purely symmetric state (s or d). $C_{es}$ presents a quadratic law at low tempeartures for a d-wave gap and for the s-wave one the typical exponential attenuation. The temperature dependence of $H_{c}$ shows a clear phase transition of second order at temperatures where the d-wave component becomes negligible. A comparison with other results and experiments is done.

cond-mat↗

arXiv1999

Analysis of the approximations used in the van Hove-BCS theory

An analysis of the different approaches used within the van Hove BCS model for the high temperature superconductors has been done. How far the employment of an asymptotic expression for the density of states underestimates the thermodynamic parameters, as for example, the critical temperature, the gap at zero temperature, and the known universal ratios of the BCS model, is discussed. Analytical expressions obtained for some thermodynamic functions are compared with the numerical results for which the exact 2D density of states has been considered. Approximate analytical expressions for the temperature dependence of the reduced gap, the superconducting electronic specific heat, and the critical magnetic field have been obtained and compared with the corresponding numerical results. The validity of the different approximations and of the equations obtained for the thermodynamic functions in the framework of the van Hove model are also analyzed.

cond-mat↗

arXiv1998

Resonant hyper-Raman scattering in spherical quantum dots

A theoretical model of resonant hyper-Raman scattering by an ensemble of spherical semiconductor quantum dots has been developed. The electronic intermediate states are described as Wannier-Mott excitons in the framework of the envelope function approximation. The optical polar vibrational modes of the nanocrystallites (vibrons) and their interaction with the electronic system are analized with the help of a continuum model satisfying both the mechanical and electrostatic matching conditions at the interface. An explicit expression for the hyper-Raman scattering efficiency is derived, which is valid for incident two-photon energy close to the exciton resonances. The dipole selection rules for optical transitions and Fröhlich-like exciton-lattice interaction are derived: It is shown that only exciton states with total angular momentum $L=0,1$ and vibrational modes with angular momentum $l_p=1$ contribute to the hyper-Raman scattering process. The associated exciton energies, wavefunctions, and vibron frequencies have been obtained for spherical CdSe zincblende-type nanocrystals, and the corresponding hyper-Raman scattering spectrum and resonance profile are calculated. Their dependence on the dot radius and the influence of the size distribution on them are also discussed.

cond-mat.mes-hall↗

arXiv1998

Exciton and confinement potential effects on the resonant Raman scattering in quantum dots

Resonant Raman scattering in semiconductor quantum dots with spherical shape is theoretically investigated. The Frohlich-like interaction between electronic states and optical vibrations has been considered. The Raman profiles are studied for the following intermediate electronic state models: (I) Uncorrelated electron-hole pairs in the strong size quantized regime, (II) Wannier-Mott excitons in an infinite potential well, and (III) Excitons in a finite confinement barrier. It is shown that the finite confinement barrier height and the electron-hole correlation determine the absolutes values of the scattering intensities and substantially modify the Raman line shape, even in the strong confinement regime.

cond-mat↗

arXiv1995

BCS-Universal Ratios within the Van Hove Scenario

The central result of BCS theory are the Universal Ratios which do not depend on physical parameters of the superconductor under study. Several attempts have been made to introduce the van Hove Scenario within BCS theory but in none of them the Universal Ratios of conventional superconductivity appear to be a number independent of parameters. This fact prevents the precise definition of a deviation from the BCS value for a particular superconductor. This concept is at the basis of several applications of BCS theory in characterizing conventional superconductors. We define a system that constitutes a weak coupling limit that retains the essential features of the high-Tc oxides and which does not differ in any essential way from other models widely used in generalizations of BCS theory to high-Tc superconductors. The difference is that we found a natural way of dealing with the mathematics of the problem so as to get Universal Ratios in the same sense as in conventional superconductivity.

cond-mat↗